How to tell if I have Dual Cert 316/316L?

[mspereira]

I have piece of pipe in my unit that should be 12" schedule 80 316L. During recent inspections, we discovered that portions of the pipe is actually 12" schedule 80S 316L. This presents a problem for me with my pressure/temperature rating. BUT if I can apply the allowable stress of 316 (not 316L) I'm good. Is there a way to tell if the piping is dual certified without the MTR's? PMI for example? Or do I just have to bite the bullet and strip the insulation and look at the markings?

 

[weldstan]

PMI won't do the job. You would need tensile tests to prove the dual 316/316L. Get the MTR, almost all 316L is dual certified.

 

[DVWE]

Not to get off topic, and someone please correct me if I'm wrong, but I don't believe stainless pipes are available in standard schedules. The "S" designates stainless pipes. 10S, 40S, 80S, etc.

For your example, there is no such thing as 12" Sch 80 316, it would only be available as 12" Sch 80S.

 

[mspereira]

DVWE, normally yes, but you can make special orders. Which it appears happened during construction of my facility.

 

[DVWE]

Understood. Unfortunately for you, weldstan is correct. Hopefully there will be some type of markings on the pipe for you. If the pipe has been cut to any length, chances are the mill markings were also cut off. I wouldn't trust a handwritten transfer mark, you need the original MTRs.

 

[racookpe1978]

It appears you need to certify the pipes. Measure the wall thickness for selected sections that represent the challenged pipes.

Once you have the as-installed thicknesses of the pipes in question, you can eliminate the "uncertainty" and "mill tolerance" subtractions needed in generic pipe code design that must subtract those margins. So, with the actual pipe wall thickness in hand for the actual assembly, and with your known corrosion and erosion allowance already established, often an "as-built" pipe network will pass a design pressure review that a "generic program" would reject.

Or, if it is close, then institute a pipe wall inspection (UT probably) check every ten years. No erosion, no problems continuing operation.

 

[EdStainless]

How do you know that it is 316L?
If you can't find the MTR then your only real option is remove a sample for mechanical testing.
The odds of it not meeting the 316 minimums are very slim, but you can't just assume.

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P.E. Metallurgy, Plymouth Tube

 

[metengr]

Remove a sample, send to the lab for a complete chemical analysis.

 

[EdStainless]

and tensile testing, you need both the chem and strength.

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P.E. Metallurgy, Plymouth Tube